Another user on the forum also uses a S3-based graphics card and has trouble running Celestia. S3 / Diamond are old and no longer made (I had one). Their OpenGL support was very basic, as OpenGL had not been implemented very widely at that point in time.
Celestia requires an OpenGL capable graphics card that supports version 1.4 of OpenGL. If your graphics card / chip does not support this, then you will not be able to happily run Celestia.
Celestia uses OpenGL in order to be "cross-platform" (it runs on Mac, Windows, AND Linux/Unix). The downside is it's OpenGL requirements.
You should be able to upgrade to a newer, fairly decent, OpenGL supporting graphics card for under $100 (US).